Wall structure for vapor generator



United States Patent D 6 Claims. (Cl. 122-406) ABSTRACT OF THEDISCLOSURE A forced circulation steam generator having a furnace wallstructure comprising a pair of parallel flow throughflow paths, eachpath including a group of tube panels, each tube panel having amultiplicity of parallel flow tubes, with tubes of the panels of eachpath being interlaced with and rigidly united to tubes of the panels ofthe other path. Provisions are made for supplying fluid in parallel flowrelation to the paths and for interconnecting the tube panels of eachpath so as to provide serial flow of fluid therethrough and so that withrespect to the longitudinal edges of the wall structure the generaldirection of flow of fluid in one path is opposite to the generaldirection of flow of fluid in the other path.

The present invention relates to improvements in the construction andarrangement of fluid heating circuits especially adapted for use in aforced circulation oncethrough steam generating unit.

The construction of a modern forced circulation oncethrough steamgenerator requires the use of a large number of parallel flow circuitsconnected between inlet and outlet headers and the provision of afurnace having gasimpervious boundary walls formed by rigidly unitedtubes. One of thefundamental problems involved with such a steamgenerator is the control of the flow through the various parallel flowcircuits over the operating load range in order that the flow in eachcircuit will be stable and the enthalpy of the fluid discharged from anyindividual circuit will be close to the average of that from allcircuits, in which case the circuit will be in a balanced flowcondition. Unbalanced flow may be caused by unequal .heat absorption inparallel flow circuits due to an unsymrnetrical arrangement of heatingsurface, slag accumula- 'tion, or part-load operation with burners outof service; or

may be due to unequal resistances caused by different lengths ofcircuits. When steam or water, or mixtures thereof, is heated inparallel flow paths provided by the furnace wall tubes or tubular panelsdisposed in the furnace, unbalanced heat and/or fluid distribution maylead to excessive localized tube metal temperatures and/ or to excessivetemperature differentials between adjacent furnace wall tubes and,thereby, to undue thermal stresses 'in the furnace wall-formingcomponents. 3

Many variations of furnace wall fluid heating circuitry have beenapplied to vapor generators of the character described..Most of thesehave one or more shortcomings including excessive thermal'stresses,uneven thermal expansion, an-d/ or lack of suflicient stability againsttransient conditionsof heat absorption inherent in the operation of avapor generator of the character described.

T he present invention solves the foregoing problems by subdividing thefurnace boundary walls into a plurality of specially arrangedfluidheating paths. In accordance with the invention, in a unit of thecharacter described each upright boundary wall of the-furnace comprisesa "pair of parallel flow through-flow paths, each path including firstand second groups of tube panels, each tube panel including amultiplicity of parallel flow tubes. Tubes 3,342,166 Patented Sept. 19,1967 of the panels of the first group in each path are juxtaposed withtubes of the panels of the first group of the other path and cooperatetherewith to form a lower portion of the wall structure, while tubes ofthe panels of the second group of said one path are juxtaposed withtubes of the panels of the second group of the other path and cooperatetherewith to form an upper portion of the wall structure. Provisions aremade for interconnecting the tube panels of the first and second groupsof each path so as to provide serial flow of fluid successively throughthe tube panels of the first group and the tube panels of the secondgroup and so that with respect to the longitudinal edges of the wallstructure the general direction of flow of fluid in said one path ineither the upper or lower portion of the wall is contrary to the generaldirection of fluid in the other path in the corresponding wall portion.

The various features of novelty which characterize the invention arepointed out with particularity in the claims anned to and forming a partof this specification. For a better understanding of the invention, itsoperating advantages and specific objects attained by its use, referenceshould be had to the accompanying drawings and descriptive matter inwhich there is illustrated and described a preferred embodiment of theinvention.

Of the drawings:

FIG. 1 is a diagrammatic view showing a furnace wall of a forced flowonce-through steam generator constructed in accordance with theinvention; and

FIG. 2 is a side view corresponding to FIG. 1.

In accordance with the invention, the furnace boundary wall fluidheating surface should be so proportioned and arranged that thetemperature of the fluid in any tube at any furnace level differs nomore than a predetermined amount from the average fluid temperature ofall furnace wall tubes at that level; that the maximum temperaturedifferential between adjacent tubes is below a predetermined criticallimit; that fluid flow unbalances are minimized; and that the tubes ofeach fluid heating pass are sufiicient in number and in inside diameteralong their length to provide adequate circulation velocities.

The structure of the drawings is intended for use as one of the uprightboundary walls of a forced flow steam generator. The wall structurecomprises a pair of parallel flow through-flow paths A and B. Path Aincludes a first group of upright coplan'ar tube panels A A A and A eachhaving a multiplicity of upright parallel tubes 10 extending betweeninlet and outlet headers 12 and 14;

while path B includes a first group of upright coplanar tube panels B BB and B each having a multiplicity of upright parallel tubes 16extending between inlet and outlet headers 18 and 20. Tubes 16 aredisposed in the spaces between tubes 10, with tubes 10 and 16 beingrigidly united, such as by metallic webs closing the intertube spacesand weld-united to the tubes, to form the lower portion of the wallstructure. Headers 12 and 14 of panels A and A are disposed somewhatbelow the corplanar tube panels A A A and A each having a multiplicityof upwardly extending parallel tubes 24 extending between inlet andoutlet headers 26 and 28 disposed exteriorly of the wall; while path Badditionally includes a second group of upright coplanar tube panels B BB and B each having a plurality of upright parallel tubes 30 extendingbetween inlet and outlet headers 32 and 34. Tubes 30 are disposed in thespaces between tubes 24, with tubes 30 and 24 being rigidly united inthe same manner as tubes 10 and 16 to form the upper portion of the wallstructure. Headers 26 and 28 of panels A and A are situated somewhatbelow the corresponding headers of panels A and A and headers 32 and 34of panels B and B are positioned somewhat below the correspondingheaders of panels B and B Inlet headers of panels A A B B inlet headersof panels A A B B outlet headers of panels A A B B and outlet headers ofpanels A A B B are respectively situated at common elevations, with theinlet headers of panels A A B B being situated intermediate outletheaders of panels A A B B and outlet headers of panels A A B B All ofthe tube panel inlet and outlet headers are so situated as not to beexposed to the high temperature heating gases. Panels A B A B A B A andB are respectively aligned with panels B5, A8, B6, A7, B7, A6, B8 andA5. the panel's thus arranged, tubes 10 of panels A and A, have upperportions interlaced with lower portions of tubes 24 of panels A and Awhile tubes 16 of panels B and B, have upper portions interlaced withlower portions of tubes of panels B and B with the tube portions sointerlaced being rigidly united to form an intermediate portion of thewall structure.

The interconnection of tube panels of fluid flow paths A and B arerespectively provided by conduits 36 and 38, each of such conduits beingdisposed exteriorly of the wall and leading from a panel outlet headerto the inlet header of the next adjacent panel of the corresponding flowpath. Parallel flow paths A and B are respectively supplied with highpresure fluid by conduits 40 and 42, which lead from a common source,and discharge to other fluid heating circuitry, not shown, by way ofconduits 44 and 46. The height of the tube panels of each path is set sothat in the event of unbalanced heat and/or fluid flow the temperatureof the fluid leaving any tube of a panel is no greater than apredetermined amount above the average temperature of the fluid leavingthe corresponding panel to prevent the possibility of undue thermalstresses between laterally adjacent tubes. Each of the conduits 40 and42 is provided with a throttle valve 48 to assist in neutralizing theeffects of unbalances in heat and/or fluid flow.

In operation high pressure fluid is passed in parallel flow relation toflow paths A and B, with the fluid in path A successively passingthrough panels A A A A A A A and A and the fluid in path B successivelypassing through panels B B B B B B B and B Along each flow path theoutflow of each tube panel is collected in the corresponding outletheader, and then mixed in the corresponding conduit 36 or 38 whilepassing to the inlet header of the next panel in the flow path. Withrespect to the longitudinal edges of the wall structure, the generaldirection of flow of fluid in path A in either the upper or lowerportion of the wall is opposite to the general direction of flow offluid in path B in the corresponding wall portion. Thus the flow offluid in path A is generally from left to right in the lower portion ofthe wall and from right to left in the upper portion of the wall, whilethe flow in path B is from right to left in the lower portion of thewall and from left to right in the upper portion of the wall. With thetube panels of the respective flow paths arranged and interconnected asabove described, the temperature of the fluid in any tube at any furnacelevel will differ no more than a predetermined safe amount from theaverage fluid temperature of all furnace wall tubes at that level andthe maximum temperature differential between adjacent tubes will bebelow a predetermined critical limit, thereby maintaining differentialexpansions in the walls within safe limits.

What is claimed is:

1. In a forced circulation fluid heating unit, a wall structure subjectto high temperature heating gases comprising a pair of parallel flowthrough-flow paths, each path comprising a group of tube panels, eachtube panel including a multiplicity of parallel flow tubes, tubes of thepanels of each path being interlaced with and rigidly united to tubes ofthe panels of the other path, means for supplying fl'uid in parallelflow relation to said paths, means interconnecting the tube panels ofeach path so as to provide serial flow of fluid therethrough and so thatwith respect to the longitudinal edges of the wall structure the generaldirection of flow of fluid in said one path is opposite to the generaldirection of flow of fluid in said other path.

2. In a forced circulation fluid heating unit, a wall structure subjectto high temperature heating gases comprising a pair of parallel flowthrough-flow paths, each path comprising a group of tube panels, eachtube panel including a multiplicity of upflow tubes arranged forparallel flow of fluid therethrough, tubes of the panels of each pathbeing interlaced with and rigidly united to tubes of the panels of theother path, means for supplying fluid in parallel flow relation to saidpaths, means interconnecting the tube panels of each path so as toprovide serial flow of fluid therethrough and so that with respect tothe longitudinal edges of the wall structure the general direction offlow of fluid in said one path is contrary to the general direction offlow of fluid in said other path.

3. In a forced circulation fluid heating unit, a wall structure subjectto high temperature heating gases comprising a pair of parallel flowthrough-flow paths, each path comprising first and second groups of tubepanels, each tube panel including a multiplicity of parallel flow tubes,tubes of the panels of the first group of each path being juxtaposedwithtubes of the panels of the first group of the other path andcooperating therewith to form a lower portion of the wall structure,tubes of the panels of the second group of said one path beingjuxtaposed with tubes of the panels of the second group of the otherpath and cooperating therewith to form an upper portion of the Wallstructure, means for supplying fluid in parallel flow relation to saidpaths, means interconnecting the tube panels of the first and secondgroups of each path so as to provide serial flow of fluid successivelythrough the tube panels of the first group and the tube panels of thesecond group and so that with respect to the longitudinal edges of thewall structure the general direction of flow of fluid in said one pathin either the upper or lower portion of the wall is opposite to thegeneral direction of flow of fluid in said other path in thecorresponding wall portion.

4. In a forced circulation fluid heating unit, a wall structure subjectto high temperature heating gases comprising a pair of parallel flowthrough-flow paths, each path comprising first and second groups of tubepanels, each tube panel including a multiplicity of parallel flow tubes,tubes of the panels of the first group of each path being interlacedwith and rigidly united to tubes of the panels of the first group of theother path and cooperating therewith to form a lower portion of the wallstructure, tubes of the panels of the second group of said one pathbeing interlaced with and rigidly united to tubes of the panels of thesecond group of the other path and cooperating therewith to form anupper portion of the wall structure, means for supplying fluid inparallel flow relation to said paths, means interconnecting the tubepanels of the first and second groups of each path so as to provideserial flow of fluid successively through the tube panels of the firstgroup and the tube panels of the second group and so that with respectto the longitudinal edges of the wall structure the general direction offlow of fluid in said one path in either the upper or lower portion ofthe wall is opposite to the general direction of flow of fluid in saidother path in the corresponding wall portion.

5. In a forced circulation fluid heating unit, awall subject to hightemperature heating gases comprising a pair of parallel flowthrough-flow paths, each path comprising first and second groups ofupflow tube panels, each tube panel including a multiplicity of parallelflow tubes, tubes of the panels of the first group of each path beinginterlaced with and rigidly united to tubes of the panels of the firstgroup of the other path and cooperating therewith to form a lowerportion of the wall structure, tubes of the panels of the second groupof said one path being interlaced with and rigidly united to tubes ofthe panels of the second group of the other path and cooperatingtherewith to form an upper portion of the wall structure, tube panels ofthe first group of said one path being aligned with the tube panels ofthe second group of the other path, tube panels of the second group ofsaid one path being aligned with tube panels of the first group of theother path, means for supplying fluid in parallel flow relation to saidpaths, means interconnecting the tube panels of the first and secondgroups of each path so as to provide serial flow of fluid successivelythrough the tube panels of the first group and the tube panels of thesecond group and so that with respect to the longitudinal edges of theWall structure the general direction of flow of fluid in said one pathin either the upper or lower portion of the wall is opposite to thegeneral direction of flow of fluid in said other path in thecorresponding wall portion.

6. In a forced circulation fluid heating unit, a wall structure subjectto high temperature heating gases comprising a pair of parallel flowthrough-flow paths, each path comprising first and second groups ofupflow tube panels, each tube panel including a multiplicity of parallelflow tubes, tubes of the panels of the first group of each path beinginterlaced with and rigidly united to tubes of the panels of the firstgroup of the other path and cooperating therewith to form a lowerportion of the wall structure, tubes of the panels of the second groupof said one path being interlaced with and rigidly united to tubes ofthe panels of the second group of the other path and cooperatingtherewith to form an upper portion of the wall structure, tubes of someof the panels of the first group of said one path having upper portionsinterlaced with lower portions of tubes of some of the panels of thesecond group of said one path, tubes of some of the panels of the firstgroup of said other path having upper portions interlaced with lowerportions of tubes of some of the panels of the second group of saidother path, means for supplying fluid in parallel flow relation to saidpaths, means interconnecting the tube panels of the first and secondgroups of each path so as to provide serial flow of fluid successivelythrough the tube panels of the first group and the tube panels of thesecond group and so that with respect to the longitudinal edges of thewall structure the general direction of flow of fluid in said one pathin either the upper or lower portion of the Wall is opposite to thegeneral direction of flow in said other path in the corresponding wallportion.

References Cited UNITED STATES PATENTS 2,989,036 6/1961 Hake et a1.122-235 3,162,179 12/1964 Strohmeyer 122-406 3,247,830 4/1966 Volger122-406 KENNETH W. SPRAGUE, Primary Examiner.

1. IN A FORCED CIRCULATION FLUID HEATING UNIT, A WALL STRUCTURE SUBJECTTO HIGH TEMPERATURE HEATING GASES COMPRISING A PAIR OF PARALLEL FLOWTHROUGH-FLOW PATHS, EACH PATH COMPRISING A GROUP OF TUBE PANELS, EACHTUBE PANEL INCLUDING A MULTIPLICITY OF PARALLEL FLOW TUBES, TUBES OF THEPANELS OF EACH PATH BEING INTERLACED WITH AND RIGIDLY UNITED TO TUBES OFTHE PANELS OF THE OTHER PATH, MEANS FOR SUPPLYING FLUID IN PARALLEL FLOWRELATION TO SAID PATHS, MEANS INTERCONNECTING THE TUBE PANELS OF EACHPATH SO AS TO PROVIDE SERIAL FLOW OF FLUID THERETHROUGH AND SO THAT WITHRESPECT TO THE LONGITUDINAL EDGES OF THE WALL STRUCTURE THE GENERALDIRECTION OF FLOW OF FLUID IN SAID ONE PATH IS OPPOSITE TO THE GENERALDIRECTION OF FLOW OF FLUID IN SAID OTHER PATH.